How hard does an erection need to be for sex to be pleasureable for a woman? is the penis supposed to be moveable or completely rock hard?

Varies: There's a lot of factors. First, obviously the base of the penis is going to have some flexibility. Position, experience of the partners willingness to try different positions, how much foreplay, lubrication, general size issues. I think both the partners and the anatomy having some flexibility is probably the ideal.

Depends ...: It's very much dependent upon the woman, as it may not be necessary for a penis to be very rigid for sex to be pleasurable for some woman. But in general, sex is easier to undertake with a more rigid penis. Don't forget about satisfaction for yourself. If rigidity is an issue please seek the input of your doctor or a urologist. Best of luck.